Near-Earth object detection technology greatly improved around 1998, so objects being detected as of 2004 could have been missed only a decade earlier due to a lack of dedicated Near-Earth sky surveys. As dedicated Near-Earth sky surveys improve, smaller and smaller asteroids are regularly being discovered. The small near-Earth asteroids 2008 TC3 and 2014 AA are the only two asteroids discovered before impacting into Earth. Scientists estimate that several dozen asteroids in the 6 to 12 meter size range fly by Earth at a distance closer than the moon every year, but only a fraction of these are actually detected.[1]

Furthermore, objects which enter and then leave Earth's atmosphere, the so-called 'Earth-grazers,' are a distinct phenomenon, inasmuch as entering the lower atmosphere can constitute an impact event rather than a close pass. Earth grazer can also be short for a body that "grazes" the orbit of the Earth, in a different context.